1. Field of the Invention
The present invention refers to a roll bar of the kind provided on topless road vehicles for protecting vehicle occupants.
2. Description of Related Art
Roll bars for protecting vehicle occupants in the case of a roll-over accident are known not only in the field of motor racing but also for topless road vehicles or convertibles (cabriolet or roadster). The roll bar can be associated with only one vehicle occupant 1 or bridge the width of the vehicle, to protect two occupants sitting side by side. The roll bar is either fixedly installed or it is abruptly raised into position and locked in place in a critical driving situation. Known roll bars consist of a U-shaped hollow tube, made of steel or light metal, having fastening points formed thereon. Load limits up to which the roll bar has to resist are predetermined by motor vehicle manufacturers for specific and typical cases of load and load directions. The main types of loads are a pressure-load acting on an apex region from above and a bending-load acting transversely to a plane defined by the roll bar. Fracture resisting requirements for the bending-load is normally less than half the fracture resisting requirements for the pressure-load. When known roll bars, consisting of a metal tube, fulfill the bending-load requirements, they are unnecessarily oversized, approximately by a factor of two, for the pressure-load requirements. Furthermore, the known tubular roll bars are heavy. The high weight requires a stable fastening to the vehicle body or, in the case of a retractable roll bar, a powerful retraction driving mechanism. In accidents where the cross-section of the tube of known roll bars is opened by abrasion, due to the fact that the vehicle slides on the roll bar, the load requirements are no longer fulfilled.
It is the object of the present invention to provide a roll bar of the type to protect occupants of a topless road vehicle which is substantially less heavy than known roll bars and whose structural design is load-oriented without being over-dimensioned for one type of load.
According to the present invention, this object is achieved by turning away from the tubular construction and using a shell construction with unitary convex portions in a substantially flat main surface, which makes it possible to provide the roll bar with an optimum load-oriented structural design, and a substantial amount of weight reduction in relation to tubular roll bars. Materials which are suitable for the roll bar of the shell-construction type are, preferably, a fibrous composite material of the kind being generally used e.g. in the field of motor racing; and also sheet steel, light-metal sheets or some other planar composite material. Modern manufacturing techniques in combination with FEM calculation of anticipated forces permit an exact load-oriented formation of the roll bar, i.e. the roll bar can be adapted to the requirements made by motor vehicle manufacturers with regard to the pressure loads and bending loads, without any necessity of over-dimensioning for one of said loads. When the advantages of shell construction are utilized consistently, a substantial amount of weight is saved, whereby it is possible to use a simpler, less heavy fastening means to the vehicle.
The roll bar of the invention is implemented as a one-piece, either single-shell component or double-shell component, with the load requirements being fulfilled in an optimum manner by the convex portions formed in the shell.
The convex portions of the main substantially flat surface of the shell are adapted to load assumptions from the very beginning, e.g. by FEM calculations with material characteristics, material thicknesses and the like. The shell comprises only the amount of material which is necessary for the respective loads, thus a maximum amount of weight is saved.
Some motor vehicle manufacturers prescribe that, in the case of an accident in which the vehicle, when rolling over, slides on the roll bar, the requirements with regard to pressure and bending loads still have to be fulfilled when abrasion occurs due to sliding friction. This requirement is fulfilled for the shell-construction roll bar by an upper abrasion zone, and/or by anti-attrition inserts. In this connection, it is preferred to provide the abrasion zone of the shell as an energy-absorbing deformation area and to attach an anti-attrition insert to the top, if desired, or, better, to provide such an insert below the abrasion zone so that it is not directly exposed to the impact forces from the very beginning of an accident involving sliding.
Up to 50% or more of the weight of a shell-construction roll bar, which is as efficient as a tubular roll bar, can be saved when said shell-construction roll bar consists of a fibrous composite material. Fibrous composite materials can be processed easily and in an ecologically harmless manner and they can be re-used later on. Glass fibers, carbon fibers or aramid fibers, with weft and warp threads in the layers of fabric, are excellently suitable materials. Plastic matrix may consist of a thermoplastic or a duroplastic material. Polyamide or PET are particularly suitable for this purpose. It is also possible in practice of the invention to use a metal foam as a matrix for fixing the layers of fabric. Thermoplastic materials have the additional advantage of being especially abrasion-resistant because these materials partially plasticize under the influence of friction (heat) and a lubricating effect is produced.
An easy and highly true-to-shape production of the roll bar is possible, even in the case of difficult cross-sectional shapes, by thermal forming, e.g. pressing under the influence of heat.
Edge regions of the shell contribute to the reinforcement of the roll bar, provided that they are implemented as convex portions. Flanges formed on the edge regions serve to connect shells in the case of a multi-shell roll bar.
Convex portions formed in the main substantially flat surface serve to optimize absorption of loads on the roll bar, the cross-section, orientation and shape of convex portions are optimized precisely with respect to load assumptions in an expedient manner by FEM calculations.
Convex portions formed in the main substantially flat surface serve to optimize absorption of loads on the roll bar. The cross-section, orientation and shape of convex portions are optimized precisely with respect to load assumptions in an expedient manner by FEM calculations.
An intentional symmetry or asymmetry of the convex portions relative to a central vertical plane of the roll bar contributes to optimize the load transmittal. In this respect, it should be pointed out that the roll bar can be implemented for taking up pressure centrally, approximately at right angles to the central plane of the roll bar, or for a load direction inclined at an oblique angle from above the center of the vehicle.
In the preferred production technology the convex portions are pressed into the substantially flat main surface from the same side of the main surface; this is especially preferred for a roll bar consisting of two shells. In the case of a single-shell roll bar it would be possible, in practice of the invention, to press the convex portions into the substantially flat main surface, alternately or in groups, from different sides of the main surface so as to increase the stability by means of a broader overall cross-section.
An abrasion zone is provided in an apex region of the shell, such abrasion zone being adapted to be consumed by an abrasion load without impairing the load capacities of the roll bar for the main loads described above. Alternatively, at least one insert of an anti-attrition material can be provided on or in the roll bar.
For optimizing the load absorbing capacity of the roll bar, it is preferred to orient weft and/or warp threads in the layers of fabric in relation to the main load directions so as to achieve a specific load absorbing behavior.
In order to conceal the technical character of the roll bar and/or in order to improve vehicle-occupant protection, an elastic cover can be provided for the roll bar.
When the shell-construction roll bar of the invention is used, fastening means for securing the roll bar in position in the vehicle can be taken into account and the increased stability or stiffness which can be achieved by use of the convex portions can be utilized in an expedient manner.
The substantially flat main surface can also have formed therein apertures for decorative or other reasons; said apertures should be formed in areas where little stress occurs under load.